Aside from any javascript errors, (which there are none I can see)... two things can prevent the image from loading. The src attribute should, by default, load an image. It doesn't have to be an actual image, but something valid should load prior to the javascript firing.
I would use a transparent image like this one: http://www.unl.edu/ucomm/templatedepend ... spixel.gifwhich is distributed with the templates.

The other necessity is that the element the image is rotated into (<img id="large1") needs to be loaded within the DOM (document object model) tree. The dom tree is created as the browser parses the source of the web page you are viewing, and allows every element within the html/xml document to be accessed. The javascript needs to be able to find the element within the dom tree when it fires, so moving the javascript call lower in your source code will increase the amount of time between when the browser parses the source of the image element and creating a referenceable node within the dom tree. I hope that makes sense.